This section provides background information related to the present disclosure. This section is not necessarily prior art.
Various industries use RF power amplifiers to amplify signals to drive voltage standing wave ratio (VSWR) loads. By way of a non-limiting example, a RF generator may include multiple RF power amplifiers. The RF power amplifiers may be used to drive a load, such as a plasma chamber. The combined power from the RF power amplifiers drives the plasma chamber to fabricate various components such as integrated circuits, solar panels, compact disks (CDs), digital versatile (or video) discs (DVDs), and the like.
Power amplifiers may have stability operating requirements. The stability requirements may include providing a fundamental frequency output signal without introducing spurious frequencies. A fundamental frequency may refer to a frequency of an input signal received by a power amplifier and/or an operating frequency of the power amplifier. The stability requirements may also include providing the fundamental frequency output signal in the presence of a load with an open circuit and/or a short circuit.
Various techniques are used to provide power amplifier stability. The techniques include series, shunt and feedback techniques. These techniques are ineffective in providing power amplifier stability for certain loads and input signal phases when operating at a fundamental frequency (e.g., 40 megahertz (MHz)). Various frequency signals other than the input signal are produced at the output of the power amplifier when the power amplifier becomes unstable. The frequencies of the various frequency signals include (i) a signal at approximately half the fundamental frequency and (ii) other signals at close in sideband frequencies (e.g., 1 kilohertz (KHz)-2 MHz) around the fundamental frequency.